Hello Anne. Knowing the context of the use of the phrases is necessary here. The "No Check" could refer to the absence of a check or bill at a restaurant or perhaps the absence of a checkmark meaning that indicates that an item has been completed on your "to do" list or requirements list. "Not Check" is most common as a part of a verb phrase such as "I did not check" my email, for instance. If you are able to share the context of the use please, I could offer a more accurate response. :) Take care, e.